1. Field of Application
The present invention relates to welding practice, and more particularly to a machine for continuous flash butt-welding of parts.
2. Description of the Prior Art
There is known a flash butt welding machine which comprises a frame with a movable clamping jaw and a stationary clamping jaw mounted thereupon, a hydraulic actuator intended for displacing the movable clamping jaw and governed by a follow-up slide valve, and devices for automatic control over the speed of flashing-off, beginning of the upset operation and upset value, said devices being provided with actuators and formed as a single unit. Irrespective of the fact that the welding process control parameters have direct bearing on the formation of a weld joint and flashing-off stability, it has been found that flash butt-welding machines sometimes fail to provide weld joints of desirable quality (cf. U.S. Pat. No. 3,790,739).
This instability in quality of weld joints may be due to:
accidental short-circuiting in the flashing-off butt ends at the moment prior to upsetting;
the deviation of the upset value from a calculated value or of the upsetting current time from a preset one.
Short circuits in the butt ends under flashing are observed prior to upset operation in the event of a considerable voltage drop in the supply circuit, as well as in the event of high power level set in the workpieces being welded due to an increase in the speed of flashing-off. Momentary periodical short circuits are impossible to be prevented because of the sluggishness of the welding machine movable plate.
A discrepancy between observed and preset, precalculated upset value results from the pressure change in the machine hydraulic system, or else due to the slippage of workpieces in the machine clamping jaws.
The deviation of the upset current time from an optimal value is observed in the event of failure in the operation of actuating means intended to cut out a welding transformer.